Imaging elements such as CCD image sensors and CMOS image sensors have respective color filters of red (R), green (G), and blue (B) arranged in mosaic fashion over an array of photoelectric conversion pixels (photodiodes). In this structure, color signals are output from the respective pixels of the color imaging elements in a manner reflecting their color filters and then signal processed so as to generate color images.
However, in the case where the imaging elements have their primary color (R, G, and B) filters arranged in mosaic fashion, two-thirds of incident light are absorbed by the respective color filters. This leads to poor utilization of light resulting in reduced sensitivity. Also, resolution is poor because only a single-color signal is obtained from each pixel. In particular, there is a possibility that false colors will become conspicuous.
PTLs 1 and 2 propose an imaging element in which three photoelectric conversion films are stacked one on top of the other. The imaging element has, for example, a pixel structure in which the three photoelectric conversion films stacked one on top of the other generate signal charges (electrons, positive holes) corresponding to the light of the blue (B), green (G), and red (R) colors, in that order, past a light incident surface. Each pixel is equipped with signal readout circuits that independently read the signal charges photo-generated by each photoelectric conversion film. In the case of this imaging element, the utilization of visible light is highly efficient because almost all incident light is photoelectrically converted. The literature proposes that images of high resolution are obtained with high sensitivity and with few conspicuous false colors thanks to the structure in which the three color signals of R, G and B are acquired from each pixel.